1. Field of the Invention
The present invention relates to a display device, and more particularly, to a display device with integrated touch screen and a method of driving the same.
2. Discussion of the Related Art
Touch screens are a type of input device that is included in image display devices such as liquid crystal display (LCD) devices, field emission displays (FEDs), plasma display panels (PDPs), electroluminescent displays (ELDs), and electrophoretic displays (EPDs), and allows a user to input predetermined information by applying a pressure (i.e., pressing or touching) to a touch sensor of a touch screen while looking at the image display device.
Particularly, the demand of display devices with integrated in-cell type touch screen, which include a plurality of built-in elements configuring the touch screen for slimming portable terminals such as smart phones and tablet personal computers (PCs), is recently increasing.
Hereinafter, driving of a general display device with integrated touch screen will be described with reference to FIG. 1.
FIG. 1 is a diagram for describing a display-to-touch crosstalk (DTX) compensation method of the general display device with integrated touch screen.
The general display device with integrated touch screen shortens a display driving time and performs touch driving for the remaining time, in one frame (60 Hz). In other words, as illustrated in FIG. 1, the general display device temporally divides a time of 16.7 ms, and performs display driving and touch driving. For example, the display driving time is limited to 10 ms, and the remaining time of 6.7 ms is used as a touch driving time in one frame.
In such a driving scheme, if a display frame rate is 60 Hz, a touch report rate is also 60 Hz similarly. In other words, the general display device with integrated touch screen transmits touch data to a system once for each sync signal defining one frame period.
For reference, a frequency at which new data are respectively transmitted to all pixels of a panel is referred to as a display frame rate, and a frequency at which touch data obtained in a touch screen are respectively transmitted to the system is referred to as a touch report rate.
However, in the general display device with integrated touch screen, when a display pattern is changed, touch raw data are changed, and due to the change of the touch raw data, DTX that causes the change of the display pattern to be inaccurately detected as a touch input occurs.
In particular, when a black pattern (0 gray scale) is changed to a white pattern (255 gray scale), a liquid crystal capacitance difference between the black pattern and the white pattern is large, easily causing DTX.
In order to remove DTX, the general display device with integrated touch screen compensates for the touch raw data by using a compensation value, which is stored in a lookup table (LUT), on the basis of data transferred from a display driver integrated chip (IC) to a touch IC.
In other words, as illustrated in FIG. 1, display information (which is displayed during one frame) of an nth frame is transferred from the display driver IC to the touch IC, and when performing touch driving of the nth frame, the touch raw data are compensated for by using the compensation value stored in the lookup table (LUT).
However, the above-described compensation method cannot obtain the touch report rate equal to or higher than the display frame rate. Also, the touch report rate higher than a frequency of 60 Hz is needed for increasing a performance of the touch screen, but a general driving scheme cannot secure the touch report rate equal to or higher than the display frame rate, and has a limitation in increasing a touch performance.